Berenil [1,3-bis(4'-amidinophenyl)triazene] binding to DNA duplexes and to a RNA duplex: evidence for both intercalative and minor groove binding properties

Bioreactivity of divalent bimetallic vanadyl and zinc complexes bis-oxalyldihydrazone ligand against microbial and human cancer series. ctDNA interaction mode

Two novel divalent bimetallic complexes were constructed from the complexation of O=V4+ and Zn2+ ions (VOL and ZnL), respectively, with diisatin oxalyldihydrazone ligand (H2L). Various spectroscopic tools were used to confirm their chemical structures (FT-IR, NMR, EI-Mass, and electronic spectra), besides, elemental analyses and conductivity features. To estimate the role of divalent metal ions in their coordination compound for developing their bio-reactivity, the free ligand H2Lox, and its complexes (VOL and ZnL) were employed spectroscopic investigations against the growth of some microbial series (fungi and bacteria) and also against three human cancer/normal cells. Furthermore, their interaction behavior against calf thymus DNA (ctDNA) was studied through viscometric and spectrophotometric studies to discover the role of O=V4+ and Zn2+ ions to determine the mode of binding with ctDNA. The inhibiting effect of H2L, VOL, and ZnL versus the titled microbial (bacterial and fungal) was built upon their inhibited zone areas in mm and the MIC concentrations in μM. Their action against the three human cancer cells' growth was evaluated by IC50 values in μM and the selectivity index in percentage. Both VOL and ZnL complexes exhibited an amazing series with three human cancer cell growth (according to the zone values in mm of inhibition, MIC in μM, and IC50 values in μM) compared to those of their uncoordinated H2L ligand. VOL demonstrated a distinguished interacting behavior with ctDNA more than that interaction of ZnL depending on the variation of the central metal ion chemical features. Within the covalent and non-covalent interaction modes, the interaction binding between H2L, VOL, and ZnL with ctDNA was discussed based on the electronic spectroscopic observation.

Adding Diversity to a Diruthenium Biscyclopentadienyl Scaffold via Alkyne Incorporation: Synthesis and Biological Studies

We report the synthesis and the assessment of the anticancer potential of two series of diruthenium biscyclopentadienyl carbonyl complexes. Novel dimetallacyclopentenone compounds (2-4) were obtained (45-92% yields) from the thermal reaction (PhCCPh exchange) of [Ru2Cp2(CO)(μ-CO){μ-η1:η3-C(Ph)═C(Ph)C(═O)}], 1, with alkynes HCCR [R = C5H4FeCp (Fc), 3-C6H4(Asp), 2-naphthyl; Cp = η5-C5H5, Asp = OC(O)-2-C6H4C(O)Me]. Protonation of 1-3 by HBF4 afforded the corresponding μ-alkenyl derivatives 5-7, in 40-86% yields. All products were characterized by IR and NMR spectroscopy; moreover, cyclic voltammetry (1, 2, 5, 7) and single-crystal X-ray diffraction (5, 7) analyses were performed on representative compounds. Complexes 5-7 revealed a cytotoxic activity comparable to that of cisplatin in A549 (lung adenocarcinoma), SW480 (colon adenocarcinoma), and ovarian (A2780) cancer cell lines, and 2, 5, 6, and 7 overcame cisplatin resistance in A2780cis cells. Complexes 2, 5, and 7 (but not the aspirin derivative 6) induced an increase in intracellular ROS levels. Otherwise, 6 strongly stabilizes and elongates natural DNA (from calf thymus, CT-DNA), suggesting a possible intercalation binding mode, whereas 5 is less effective in binding CT-DNA, and 7 is ineffective. This trend is reversed concerning RNA, and in particular, 7 is able to bind poly(rA)poly(rU) showing selectivity for this nucleic acid. Complexes 5-7 can interact with the albumin protein with a thermodynamic signature dominated by hydrophobic interactions. Overall, we show that organometallic species based on the Ru2Cp2(CO)x scaffold (x = 2, 3) are active against cancer cells, with different incorporated fragments influencing the interactions with nucleic acids and the production of ROS.

Diminazene aceturate uses different pathways to induce relaxation in healthy and atherogenic blood vessels

Diminazene aceturate (DIZE), a putative angiotensin-converting enzyme 2 (ACE2) activator, elicits relaxation in various animal models. This study aimed to determine the relaxing mechanisms in internal iliac arteries utilised by DIZE in healthy and atherogenic rabbit models. Studies were conducted on internal iliac artery rings retrieved from male New Zealand White rabbits fed a 4-week healthy control (n = 24) or atherogenic diet (n = 20). To investigate pathways utilised by DIZE to promote arterial relaxation, a DIZE dose response [10^-9.0 M - 10^-5.0 M] was performed on pre-contracted rings incubated with pharmaceuticals that target: components of the renin-angiotensin system; endothelial- and vascular smooth muscle-dependent mechanisms; protein kinases; and potassium channels. ACE2 expression was quantified by immunohistochemistry analysis following a 2 hr or 4 hr DIZE incubation. DIZE significantly enhanced vessel relaxation in atherogenic rings at doses [10^-5.5 M] (p < 0.01) and [10^-5.0 M] (p < 0.0001), when compared to healthy controls. Comprehensive results from functional isometric studies determined that DIZE causes relaxation via different mechanisms depending on pathology. For the first time, we report that in healthy blood vessels DIZE exerts its direct relaxing effect through ACE2/AT₂R and NO/sGC pathways; however, in atherogenesis this switches to MasR, arachidonic acid pathway (i.e., COX1/2, EET and DHET), MCLP, Ca²⁺ activated voltage channels, AMPK and ERK1/2. Moreover, quantitative immunohistochemical analysis demonstrated that DIZE increases artery ACE2 expression in a time dependent manner. We provide a detailed investigation of DIZE's mechanisms and demonstrate for the first time that in healthy and atherogenic arteries DIZE provides beneficial effects through directly inducing relaxation, albeit via different pathways.

Is Diminazene an Angiotensin-Converting Enzyme 2 (ACE2) Activator? Experimental Evidence and Implications

Antiprotozoal veterinary drug diminazene aceturate (DIZE) has been proposed to be an angiotensin-converting enzyme 2 (ACE2) activator. Since then, DIZE was used in dozens of experimental studies, but its mechanism of action attributed to ACE2 activation and enhanced formation of angiontensin-(1-7) [Ang-(1-7)] from Ang II was not carefully verified. The aim of this study was to confirm the effect of DIZE on catalytic activity of ACE2 and extend it to other peptidases involved in formation and degradation of Ang-(1-7). Concentration-dependent effect of DIZE on the initial rate of a fluorogenic substrate hydrolysis by human and mouse recombinant ACE2 was measured at assay conditions imitating that of the original report, but no activation of ACE2 was documented. Similar results were obtained with a more physiologically relevant assay buffer. In addition, DIZE did not affect activity of recombinant neprilysin, neurolysin, thimet oligopeptidase, and ACE. Efficiency of the fluorogenic substrate hydrolysis (Vmax/Km value) by ACE2 in response to different concentrations of DIZE was also measured, but no substantial effects were documented. Likewise, DIZE failed to enhance the hydrolysis of ACE2 endogenous substrate Ang II. Identity of the commercial recombinant ACE2 variants used in these experiments was confirmed by inhibition with two well characterized inhibitors (DX600 and MLN4760), activation by NaCl, and Western Blotting using validated antibodies. These observations challenge the widely accepted notion about the molecular mechanism of DIZE action and call for not ascribing this molecule as an ACE2 activator. SIGNIFICANCE STATEMENT: DIZE has been proposed and widely used in experimental studies as an ACE2 activator. The detailed in vitro pharmacological studies failed to confirm that DIZE is an ACE2 activator. In addition, DIZE did not substantially affect the activity of other peptidases involved in formation and degradation of angiotensin-(1-7). Researchers should refrain from calling DIZE an ACE2 activator. Other mechanisms are responsible for the therapeutic benefits attributed to DIZE.

Thermodynamic Factors That Drive Sequence-Specific DNA Binding of Designed, Synthetic Minor Groove Binding Agents

Ken Breslauer began studies on the thermodynamics of small cationic molecules binding in the DNA minor groove over 30 years ago, and the studies reported here are an extension of those ground-breaking reports. The goals of this report are to develop a detailed understanding of the binding thermodynamics of pyridine-based sequence-specific minor groove binders that have different terminal cationic groups. We apply biosensor-surface plasmon resonance and ITC methods to extend the understanding of minor groove binders in two directions: (i) by using designed, heterocyclic dicationic minor groove binders that can incorporate a G•C base pair (bp), with flanking AT base pairs, into their DNA recognition site, and bind to DNA sequences specifically; and (ii) by using a range of flanking AT sequences to better define molecular recognition of the minor groove. A G•C bp in the DNA recognition site causes a generally more negative binding enthalpy than with most previously used pure AT binding sites. The binding is enthalpy-driven at 25 °C and above. The flanking AT sequences also have a large effect on the binding energetics with the -AAAGTTT- site having the strongest affinity. As a result of these studies, we now have a much better understanding of the effects of the DNA sequence and compound structure on the molecular recognition and thermodynamics of minor groove complexes.

5-Substituted 3, 3', 4', 7-tetramethoxyflavonoids - A novel class of potent DNA triplex specific binding ligands

Herein, we present a class of potent triplex DNA binding ligands derived from the natural product quercetin, which is the first of its kind that has ever been reported in the literature. The binding of 5-substituted quercetin derivatives (3, 3', 4', 7-tetramethoxyflavonoids) to triplex and duplex DNA was investigated using several biophysical tools, including thermal denaturation monitored by UV, circular dichroism, differential scanning calorimetry, and isothermal titration calorimetry. Experimental data reveal that several 5-substituted 3, 3', 4', 7-tetramethoxyflavonoids have remarkable effects on binding to DNA triple helices, and they do not influence the double-helical DNA structures. A few derivatives such as compounds 5 and 7 have comparable (if not better) binding affinities to neomycin, a well-known DNA triplex binding ligand, under the same conditions. The amino-containing side chains at the 5-position of 3, 3', 4', 7-tetramethoxyflavonoids are crucial for the observed binding affinity and specificity.

Porphyrin induced structural destabilization of a parallel DNA G-quadruplex in human MRP1 gene promoter

Porphyrins are among the first ligands that have been tested for their quadruplex binding and stabilization potential. We report the differential interaction of the positional cationic porphyrin isomers TMPyP3 and TMPyP4 with a parallel G-quadruplex (GQ) formed by 33-mer (TP) regulatory sequence present in the promoter region of the human multidrug resistance protein 1 (MRP1) transporter gene. This GQ element encompasses the three evolutionary conserved SP1 transcription factor binding sites. Taking into account that SP1 binds to a non-canonical GQ motif with higher affinity than to a canonical duplex DNA consensus motif, it is suggestive that GQ distortion by cationic porphyrin will have important implications in the regulation of MRP1 expression. Herein, we employed biophysical analysis using circular dichroism, visible absorption, UV-thermal melting and steady-state fluorescence spectroscopy, reporting destabilization of MRP1 GQ by cationic porphyrins. Results suggest that TMPyP4 and TMPyP3 interact with GQ with a binding affinity of 10⁶ to 10⁷  M^-1 . Thermodynamic analysis indicated a significant decrease in melting temperature of GQ (ΔTm of 15.5°C-23.5°C), in the presence of 2 times excess of porphyrins. This study provides the biophysical evidence indicating the destabilisation of a parallel DNA G-quadruplex by cationic porphyrins.

Profound Nanoscale Structural and Biomechanical Changes in DNA Helix upon Treatment with Anthracycline Drugs

In our study, we describe the outcomes of the intercalation of different anthracycline antibiotics in double-stranded DNA at the nanoscale and single molecule level. Atomic force microscopy analysis revealed that intercalation results in significant elongation and thinning of dsDNA molecules. Additionally, using optical tweezers, we have shown that intercalation decreases the stiffness of DNA molecules, that results in greater susceptibility of dsDNA to break. Using DNA molecules with different GC/AT ratios, we checked whether anthracycline antibiotics show preference for GC-rich or AT-rich DNA fragments. We found that elongation, decrease in height and decrease in stiffness of dsDNA molecules was highest in GC-rich dsDNA, suggesting the preference of anthracycline antibiotics for GC pairs and GC-rich regions of DNA. This is important because such regions of genomes are enriched in DNA regulatory elements. By using three different anthracycline antibiotics, namely doxorubicin (DOX), epirubicin (EPI) and daunorubicin (DAU), we could compare their detrimental effects on DNA. Despite their analogical structure, anthracyclines differ in their effects on DNA molecules and GC-rich region preference. DOX had the strongest overall effect on the DNA topology, causing the largest elongation and decrease in height. On the other hand, EPI has the lowest preference for GC-rich dsDNA. Moreover, we demonstrated that the nanoscale perturbations in dsDNA topology are reflected by changes in the microscale properties of the cell, as even short exposition to doxorubicin resulted in an increase in nuclei stiffness, which can be due to aberration of the chromatin organization, upon intercalation of doxorubicin molecules.

Repurposed drug candidates for antituberculosis therapy

Antibiotics have been a key part of clinical treatments for more than 70 years. Long-term use of antimicrobial treatments has led to the development of severe bacterial resistance, which has become increasingly serious due to antibiotic abuse, resulting in the treatment of bacterial infections becoming challenging. The repurposing of approved drugs presents a promising strategy to address current bottlenecks in the development of novel antibacterial agents. Drug repurposing is a cost-effective emerging strategy, which aims to treat resistant infectious diseases by identifying known drugs with predicted efficacy for diseases other than the target disease. This strategy has potential in the treatment of tuberculosis (TB), particularly drug-resistant TB. In recent years, a panel of drugs approved for clinical use or clinical trials, such as linezolid, vancomycin and celecoxib, have been found to have anti-TB activities. However, the utility of drug repurposing is limited by the number of candidate compounds and their low activities. The low activities of repurposed drugs have slowed the development of a drug-repurposing strategy for anti-TB drugs. The present review discusses progress in the discovery of new anti-TB agents through drug repurposing since 2014. We also discuss the challenges faced and analyze the innovative ways that are being used to overcome these difficulties. This review may provide a useful guide for researchers in the field of drug repurposing.

The potential actions of angiotensin-converting enzyme II (ACE2) activator diminazene aceturate (DIZE) in various diseases

The renin angiotensin system (RAS) regulates fluid balance, blood pressure and maintains vascular tone. The potent vasoconstrictor angiotensin II (Ang II) produced by angiotensin-converting enzyme (ACE) comprises the classical RAS. The non-classical RAS involves the conversion of Ang II via ACE2 into the vasodilator Ang (1-7) to counterbalance the effects of Ang II. Furthermore, ACE2 converts AngA into another vasodilator named alamandine. The over activation of the classical RAS (increased vasoconstriction) and depletion of the non-classical RAS (decreased vasodilation) results in vascular dysfunction. Vascular dysfunction is the leading cause of atherosclerosis and cardiovascular disease (CVD). Additionally, local RAS is expressed in various tissues and regulates cellular functions. RAS dysregulation is involved in other several diseases such as inflammation, renal dysfunction and even cancer growth. An approach in restoring vascular dysfunction and other pathological diseases is to either increase the activity of ACE2 or reduce the effect of the classical RAS by counterbalancing Ang II effects. The antitrypanosomal agent, diminazene aceturate (DIZE), is one approach in activating ACE2. DIZE has been shown to exert beneficial effects in CVD experimental models of hypertension, myocardial infarction, type 1 diabetes and atherosclerosis. Thus, this review focuses on DIZE and its effect in several tissues such as blood vessels, cardiac, renal, immune and cancer cells.

Mechanisms of NMDA receptor inhibition by diarylamidine compounds

Pentamidine, diminazene and 4',6-diamidino-2-phenylindole (DAPI) are antiprotozoal diarylamidine compounds. In the present work, we have studied their action on native N-methyl-D-aspartate (NMDA) receptors in rat hippocampal pyramidal neurons. All three compounds inhibited NMDA receptors at -80 mV holding voltage with IC₅₀ of 0.41 ± 0.08, 13 ± 3 and 3.1 ± 0.6 μM, respectively. The inhibition by pentamidine was strongly voltage-dependent, while that of DAPI was practically voltage-independent. Inhibition by diminazene had both voltage-dependent and voltage-independent components. Diminazene and DAPI demonstrated tail currents and overshoots suggesting "foot-in-the-door" mechanism of action. In contrast, pentamidine was partially trapped in the closed NMDA receptor channels. Such difference in the mechanism of action can be explained by the difference in the 3D structure of compounds. In the pentamidine molecule, two benzamidine groups are connected with a flexible linker, which allows the molecule to fold up and fit in the cavity of a closed NMDA receptor channel. Diminazene and DAPI, in contrast, have an extended form and could not be trapped.

How a linear triazene photoisomerizes in a volume-conserving fashion

Understanding deactivation mechanisms of functional groups is a key step to design novel photo-active devices and molecular imaging agents. Here, we elucidate the photochemistry of linear triazenes, an extended analogue of the photo-switchable azo group, exemplarily for the widely used DNA-minor-groove binder berenil. Combining ultrafast spectroscopy and ab initio calculations unveils that the E-azo,s-trans structure of berenil predominates in the gas phase and in aqueous solution, and ADC(2) intrinsic reaction coordinate calculations disclose that the excited-state relaxation to the S1 minima/conical intersections follows a two-step mechanism: N[double bond, length as m-dash]N bond stretching followed by a bicycle-pedal rotation in the triazene bridge. Furthermore, studying the ground-state pathways shows that a fraction of the molecules relaxes back to the E-azo,s-trans isomer while the other part photoisomerizes to the Z-azo,s-trans via a hula-twist motion, as evidenced by experimental quantum yields of Φ ≈ 0.5 found for berenil in water, ethylene glycol, or bound to β-trypsin. Moreover, our studies show that while the excited-state relaxation is insensitive to the environment, the ground-state dynamics depend on biomolecular binding partners.

Probing drug-DNA interactions using super-resolution force spectroscopy

Atomic magnetometry and ultrasound, as individual techniques, have been used extensively in various physical, chemical, and biomedical fields. Their combined application, however, has been rare. We report that super-resolution force spectroscopy, which is based on the integration of the two techniques, can find unique biophysical applications in studying drug-DNA interactions. The precisely controlled ultrasound generates acoustic radiation force on the biological systems labeled with magnetic microparticles. A decrease in the magnetic signal, measured by an automated atomic magnetometer, indicates that the acoustic radiation force equals the binding force of the biological system. With 0.5 pN force resolution, we were able to precisely resolve three small molecules binding with two DNA sequences and quantitatively reveal the effect of a single hydrogen bond. Our results indicate that the increases in DNA binding force caused by drug binding correlate with the enthalpy instead of free energy, thus providing an alternative physical parameter for optimizing chemotherapeutic drugs.

Ultrafast Dynamics of a Triazene: Excited-State Pathways and the Impact of Binding to the Minor Groove of DNA and Further Biomolecular Systems

Many synthetic DNA minor groove binders exhibit a strong increase in fluorescence when bound to DNA. The pharmaceutical-relevant berenil (diminazene aceturate) is an exception with an extremely low fluorescence quantum yield (on the order of 10^-4). We investigate the ultrafast excited-state dynamics of this triazene by femtosecond time-resolved fluorescence experiments in water, ethylene glycol, and buffer and bound to the enzyme β-trypsin, the minor groove of AT-rich DNA, and G-quadruplex DNA. Ab initio calculations provide additional mechanistic insight. The complementing studies unveil that the excited-state motion initiated by ππ* excitation occurs in two phases: a subpicosecond phase associated with the lengthening of the central N═N double bond, followed by a bicycle-pedal-type motion of the triazene bridge, which is almost volume-conserving and can proceed efficiently within only a few picoseconds even under spatially confined conditions. Our results elucidate the excited-state relaxation mechanism of aromatic triazenes and explain the modest sensitivity of the fluorescence quantum yield of berenil even when it is bound to various biomolecules.

Linker dependent intercalation of bisbenzimidazole-aminosugars in an RNA duplex; selectivity in RNA vs. DNA binding

Neomycin and Hoechst 33258 are two well-known nucleic acid binders that interact with RNA and DNA duplexes with high affinities respectively. In this manuscript, we report that covalent attachment of bisbenzimidazole unit derived from Hoechst 33258 to neomycin leads to intercalative binding of the bisbenzimidazole unit (oriented at 64-74° with respected to the RNA helical axis) in a linker length dependent manner. The dual binding and intercalation of conjugates were supported by thermal denaturation, CD, LD and UV-Vis absorption experiments. These studies highlight the importance of linker length in dual recognition by conjugates, for effective RNA recognition, which can lead to novel ways of recognizing RNA structures. Additionally, the ligand library screens also identify DNA and RNA selective compounds, with compound 9, containing a long linker, showing a 20.3°C change in RNA duplex Tm with only a 13.0°C change in Tm for the corresponding DNA duplex. Significantly, the shorter linker in compound 3 shows almost the reverse trend, a 23.8°C change in DNA Tm, with only a 9.1°C change in Tm for the corresponding RNA duplex.

Unraveling the physical chemistry and the mixed binding modes of complex DNA ligands by single molecule stretching experiments

In this work we present a complete methodology to unravel the physical chemistry and the mixed binding modes of complex DNA ligands.

Glycosaminoglycans are potential pharmacological targets for classic DNA minor groove binder drugs berenil and pentamidine

It is shown that the antiprotozoal drugs berenil and pentamidine, conventional minor groove binders of DNA, form non-covalent complexes with polyanionic glycosaminoglycans.

3-Acetyl-bis(2-chloro-4-nitrophenyl)triazene is a potent antitumor agent that induces oxidative stress and independently activates the stress-activated protein kinase/c-Jun NH2-terminal kinase pathway

Previously, we described the synthesis and biological activity of a new class of anticancer molecules that preferentially target malignant cells and may serve as potential antitumor agents. Among several synthesized agents, we selected 3-acetyl-1,3-bis(2-chloro-4-nitrophenyl)-1-triazene (8b) as a representative of the group of 4-nitro-substituted 1,3-diaryltriazenes. The aim of this study was to further investigate the mechanism of cell response to the 8b compound. The HeLa human cervical carcinoma cell line was used as an experimental model to further investigate the mechanism of cell response to the 8b compound. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay was used to address cell survival, and western blot (immunoblotting) was used for the expression of relevant proteins after 8b drug exposure. The pretreatment of HeLa cells with salubrinal, a specific inhibitor of endoplasmic reticulum (ER) stress, confirmed the importance of ER stress in apoptosis induced by 8b. We also demonstrate that 8b triggers the activation of stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK) in a time-dependent and dose-dependent manner. Moreover, the inhibition of SAPK/JNK activity by JNK II before 8b treatment increased the survival rate of HeLa cells relative to survival in the presence of 8b alone, indicating the importance of this kinase in cell death. The simultaneous inhibition of ER stress induction and SAPK/JNK activation increased the survival of HeLa cells upon 8b treatment more than inhibition of both pathways independently, suggesting the separate triggering of both signaling pathways. Our data indicate that cytotoxic activity of the novel compound 8b is based on its ability to induce ER stress and SAPK/JNK signaling pathways independently, driving cells to cell death.

Interaction of 6 mercaptopurine with calf thymus DNA--deciphering the binding mode and photoinduced DNA damage

DNA is one of the major intracellular targets for a wide range of anticancer and antibiotic drugs. Elucidating the binding between small molecules and DNA provides great help in understanding drug-DNA interactions and in designing of new and promising drugs for clinical use. The ability of small molecules to bind and interfere with DNA replication and transcription provides further insight into how the drugs control the expression of genes. Interaction of an antimetabolite anticancer drug 6mercaptopurine (6MP) with calf thymus DNA was studied using various approaches like UV-visible spectroscopy, fluorescence spectroscopy, CD, viscosity and molecular docking. UV-visible spectroscopy confirmed 6MP-DNA interaction. Steady state fluorescence experiments revealed a moderate binding constant of 7.48×10³ M⁻¹ which was consistent with an external binding mode. Competitive displacement assays further confirmed a non-intercalative binding mode of 6MP which was further confirmed by CD and viscosity experiments. Molecular docking further revealed the minimum energy conformation (−119.67 kJ/mole) of the complex formed between DNA and 6MP. Hence, the biophysical techniques and in-silico molecular docking approaches confirmed the groove binding/electrostatic mode of interaction between 6MP and DNA. Further, photo induced generation of ROS by 6MP was studied spectrophotometrically and DNA damage was assessed by plasmid nicking and comet assay. There was a significant increase in ROS generation and consequent DNA damage in the presence of light.

Diminazene or berenil, a classic duplex minor groove binder, binds to G-quadruplexes with low nanomolar dissociation constants and the amidine groups are also critical for G-quadruplex binding

Diminazene or berenil is known to be an AT-rich DNA minor groove binder with micromolar dissociation constant. Here, we show that DMZ binds to G-quadruplexes withK_das low as 1 nM.

Diminazene aceturate enhances angiotensin-converting enzyme 2 activity and attenuates ischemia-induced cardiac pathophysiology

Angiotensin-converting enzyme 2 (ACE2) plays a critical role against myocardial infarction (MI). We hypothesized that activation of intrinsic ACE2 would be protective against ischemia-induced cardiac pathophysiology. Diminazene aceturate (DIZE), a small molecule ACE2 activator, has been used to evaluate this hypothesis. DIZE (15 mg/kg per day, s.c.) was injected 2 days before MI surgery and continued throughout the study period. MI rats showed a 62% decrease in fractional shortening (%; control, 51.1±3.2; DIZE alone, 52.1±3.2; MI, 19.1±3.0), a 55% decrease in contractility (dP/dtmax mm Hg/s; control, 9480±425.3; DIZE alone, 9585±597.4; MI, 4251±657.7), and a 27% increase in ventricular hypertrophy (mg/mm; control, 26.5±1.5; DIZE alone, 26.9±1.4; MI, 33.4±1.1). DIZE attenuated the MI-induced decrease in fractional shortening by 89%, improved dP/dtmax by 92%, and reversed ventricular hypertrophy by 18%. MI also significantly increased ACE and angiotensin type 1 receptor levels but decreased ACE2 activity by 40% (control, 246.2±25.1; DIZE alone, 254.2±20.6; MI, 148.9±29.2; RFU/min), which was reversed by DIZE treatment. Thus, DIZE treatment decreased the infarct area, attenuated LV remodeling post-MI, and restored normal balance of the cardiac renin-angiotensin system. In addition, DIZE treatment increased circulating endothelial progenitor cells, increased engraftment of cardiac progenitor cells, and decreased inflammatory cells in peri-infarct cardiac regions. All of the beneficial effects associated with DIZE treatment were abolished by C-16, an ACE2 inhibitor. Collectively, DIZE and DIZE-like small molecules may represent promising new therapeutic agents for MI.

Diminazene attenuates pulmonary hypertension and improves angiogenic progenitor cell functions in experimental models

RATIONALE

Studies have demonstrated that angiotensin-converting enzyme 2 (ACE2) plays a protective role against lung diseases, including pulmonary hypertension (PH). Recently, an antitrypanosomal drug, diminazene aceturate (DIZE), was shown to exert an "off-target" effect of enhancing the enzymatic activity of ACE2 in vitro.

OBJECTIVES

To evaluate the pharmacological actions of DIZE in experimental models of PH.

METHODS

PH was induced in male Sprague Dawley rats by monocrotaline, hypoxia, or bleomycin challenge. Subsets of animals were simultaneously treated with DIZE. In a separate set of experiments, DIZE was administered after 3 weeks of PH induction to determine whether the drug could reverse PH.

MEASUREMENTS AND MAIN RESULTS

DIZE treatment significantly prevented the development of PH in all of the animal models studied. The protective effects were associated with an increase in the vasoprotective axis of the lung renin-angiotensin system, decreased inflammatory cytokines, improved pulmonary vasoreactivity, and enhanced cardiac function. These beneficial effects were abolished by C-16, an ACE2 inhibitor. Initiation of DIZE treatment after the induction of PH arrested disease progression. Endothelial dysfunction represents a hallmark of PH pathophysiology, and growing evidence suggests that bone marrow-derived angiogenic progenitor cells contribute to endothelial homeostasis. We observed that angiogenic progenitor cells derived from the bone marrow of monocrotaline-challenged rats were dysfunctional and were repaired by DIZE treatment. Likewise, angiogenic progenitor cells isolated from patients with PH exhibited diminished migratory capacity toward the key chemoattractant stromal-derived factor 1α, which was corrected by in vitro DIZE treatment.

CONCLUSIONS

Our results identify a therapeutic potential of DIZE in PH therapy.

Diamidinium and iminium aromatics as new aggregators of the bacterial signaling molecule, c-di-GMP

C-di-GMP has emerged as an important bacterial signaling molecule that is involved in biofilm formation. Small molecules that can form biologically inactive complexes with c-di-GMP have the potential to be used as anti-biofilm agents. Herein, we report that water-soluble diamidinium/iminium aromatics (such as berenil), which are traditionally considered as minor groove binders of nucleic acids, are capable of aggregating c-di-GMP into G-quadruplexes via π-stacking interactions.

Development of a nanoparticulate formulation of diminazene to treat African trypanosomiasis

There is a real need to develop new therapeutic strategies for African trypanosomiasis infections. In our study, we developed a new drug delivery system of diminazene (DMZ), a trypanocidal drug registered for veterinary use. This drug candidate presents a limited efficacy, a poor affinity for brain tissue and instability. The development of colloidal formulations based on a porous cationic nanoparticle with an oily core ((70)DGNP(+)), has potentially two advantages: stabilization of the drug and potential targeting of the parasite. We analyzed two processes of drug loading: in process (DMZ was added during the preparation of (70)DGNP(+) at 80 °C) and post-loading (DMZ was mixed with a (70)DGNP(+) solution at room temperature). Poor stability of the drug was observed using the in process technique. When using the post-loading technique over 80% drug entrapment efficiency was obtained at a ratio of DMZ:phospholipids (wt:wt) < 5%. Moreover, DMZ loaded into (70)DGNP(+) was found to be protected against oxidation and was stable for at least six months at 4 °C. Finally, in vitro tests on T.b. brucei showed an increased efficacy of DMZ loaded in (70)DGNP(+).

Revisiting the association of cationic groove-binding drugs to DNA using a Poisson-Boltzmann approach

Proper modeling of nonspecific salt-mediated electrostatic interactions is essential to understanding the binding of charged ligands to nucleic acids. Because the linear Poisson-Boltzmann equation (PBE) and the more approximate generalized Born approach are applied routinely to nucleic acids and their interactions with charged ligands, the reliability of these methods is examined vis-à-vis an efficient nonlinear PBE method. For moderate salt concentrations, the negative derivative, SK(pred), of the electrostatic binding free energy, DeltaG(el), with respect to the logarithm of the 1:1 salt concentration, [M(+)], for 33 cationic minor groove drugs binding to AT-rich DNA sequences is shown to be consistently negative and virtually constant over the salt range considered (0.1-0.4 M NaCl). The magnitude of SK(pred) is approximately equal to the charge on the drug, as predicted by counterion condensation theory (CCT) and observed in thermodynamic binding studies. The linear PBE is shown to overestimate the magnitude of SK(pred), whereas the nonlinear PBE closely matches the experimental results. The PBE predictions of SK(pred) were not correlated with DeltaG(el) in the presence of a dielectric discontinuity, as would be expected from the CCT. Because this correlation does not hold, parameterizing the PBE predictions of DeltaG(el) against the reported experimental data is not possible. Moreover, the common practice of extracting the electrostatic and nonelectrostatic contributions to the binding of charged ligands to biopolyelectrolytes based on the simple relation between experimental SK values and the electrostatic binding free energy that is based on CCT is called into question by the results presented here. Although the rigid-docking nonlinear PB calculations provide reliable predictions of SK(pred), at least for the charged ligand-nucleic acid complexes studied here, accurate estimates of DeltaG(el) will require further development in theoretical and experimental approaches.